1. Field of the Invention
The present invention pertains generally to wheel suspension systems and, more particularly, to an intra-hub rear suspension system for a motorcycle.
2. Description of the Prior Art
Many motorcycles have rigid frames. Such motorcycles could benefit from an intra-hub rear suspension system. Other motorcycles have used rear shock absorbing systems, or suspensions, comprised of external shock absorbers or springs that are mounted outboard of the rear axle to provide for dampened, load-induced movement of the rear wheel relative to the rear frame. For example, some motorcycle rear frames include a shock absorbing swing-arm coupled to a pivot axle. However, these outboard suspension systems exhibit some mechanical inefficiency and clutter the appearance of the motorcycle.
Additionally, many suspension systems do not guide the rear wheel along an arc that is centered on the drive sprocket connected to the drive chain or drive belt. Such suspension systems undesirably allow for relative movement of the rear wheel with respect to the rear frame and thereby alter the tension of the drive chain during operation of the motorcycle. The result is high wear and inefficiency of the drive chain system.
FIG. 1 shows a motorcycle 10 including a frame 15 and a rear wheel 20 that may include an intra-hub rear suspension according to this invention. As shown, the motorcycle further includes a drive sprocket 11 that is coupled to a wheel sprocket 21 via a suitable drive belt or drive chain 12. Ideally, the motorcycle 10 will include a suspension system that permits the rear wheel 20 to move along an arc 27 that is centered about the drive sprocket 11.
A prior art intra-hub wheel suspension is disclosed in U.S. Pat. No. 5,390,757, entitled “Intra-Wheel Rear Suspension System for Motorcycles,” assigned to Dew Manufacturing Company, Inc., the assignee of the present invention. The Smith patent is hereby incorporated by reference in its entirety as if fully set forth herein.
FIGS. 2 and 3 are representative of the intra-wheel rear suspension system disclosed in the Smith patent. The item numbers used generally correspond to those used within the Smith patent, with the addition of a prime, e.g. 50′ corresponds to item 50. As shown, the Smith patent discloses an intra-wheel rear suspension system includes a shock absorber mechanism 50′ that is part of an inner hub (not shown here) that rotatably supports an outer hub (also not shown here) connected to a rim and tire.
The shock absorber mechanism 50′ comprises two main parts, an inner carrier assembly 76′ with a rear shaft 40′ extending to either side thereof, and an outer track frame 52′ that moves relative to the inner carrier assembly 76′. Two pairs of nested load springs 94′/96′ are captured between the inner carrier assembly 76′ and the outer track frame 52′. The load springs 94′/96′ serve as shock absorbers, i.e. they are compressed when the road surface pushes the rear wheel upward relative to the motorcycle frame or when inertia pushes the motorcycle frame downward relative to the rear wheel. Another pair of smaller rebound springs 102′ are captured on the opposite side of the assembly. The smaller rebound springs 102′ function as return and dampening springs.
The rear shaft 40′, the inner carrier assembly 76′, and certain other components (not shown for clarity), are fixedly attached to the lateral arms of the motorcycle's rear frame. The outer track frame 52′, along with certain other components that are rotatably supported by the outer track frame 52′ (such as an outer hub, a rim, and a tire) can move up and down relative to the inner carrier assembly 76′.
The Smith patent's shock absorber mechanism 50′ beneficially provided for arcuate movement 27 as illustrated by FIG. 1 (in exaggeration) and FIG. 3. In particular, the inner carrier assembly 76′ included a plurality of rollers 74′, 84′, 86′ and the outer track frame 52′ included a pair of grooved cam surfaces 70′, 72′ that are curved or arcuate. The grooved cam surfaces 70′, 72′ engaged the rollers 74′, 84′, 86′ such that the outer track frame 52′ moved in an arc 27 relative to the inner carrier assembly 76′. This arcuate movement was a significant advancement in that it maintained a constant tension on the drive belt (not shown). However, the prior art shock absorber mechanism 50′ disclosed in the Smith patent also exhibited certain deficiencies owing to its design and construction. In particular, because of the lateral play between the grooved cam surfaces 70′, 72′ and the rollers 74′, 84′, 86′, the Smith patent's shock absorber mechanism 50′ also permitted some degree of lateral and/or torsional movement, or play, about its vertical axis as suggested in exaggeration by arrows 48 and 49 of FIG. 2. Such movement, of course, is undesirable. In operational tests, the angular movement was observed to be 0.015 inches or more.
Consequently, there remains a need for an intra-wheel rear suspension system that addresses the problem of angular movement or torsional play.
Therefore, it is an object of the present invention (1) to provide an improved suspension system that is entirely contained within the hub of a wheel of a vehicle; (2) to provide an improved suspension system for the rear wheel of a motorcycle; (3) to provide an improved suspension for the rear wheel of a motorcycle that will increase chain life and decrease wear and maintenance requirements; (4) to provide a suspension system for the rear wheel of a motorcycle that provides relative movement of the wheel in an arc about the drive sprocket of the motorcycle; (5) to provide a motorcycle suspension having extended wear characteristics; (6) to provide a motorcycle suspension having an uncluttered appearance; and (7) to provide a design and method for an intra-wheel rear suspension system that addresses the problem of angular movement or torsional play.